The present disclosure relates generally to locating and shimming one part relative to another part, such as parts constructed and assembled for aircraft or ships.
Determinate assembly (DA) is a method of aligning parts using mating physical features. Typically, coordinating holes which are placed on each part or structure are used to take advantage of the ability to install temporary fasteners to hold the parts together. The parts of a determinate assembly are sometimes required to be joined together with an accuracy that is within a specified tolerance.
During the assembly of aircraft parts, it may be necessary to affix parts to one another such that any gap between the two parts is occupied by filler material, commonly referred to as a “shim”. Typically, this is done by temporarily installing the parts and checking to see if any gaps exist. When the gap exceeds a specified tolerance, a shim or similar filler may be inserted into the gap in order to assure a within-tolerance fit between the parts. Shims can be used to fill voids discovered during an assembly process. Voids are typically formed by the misalignment of parts during assembly or by variation in manufacture of the parts being assembled. Although mostly used on an as-needed basis during manufacturing, some shims are called out on drawings as part of the manufacturing process. Shims are used throughout the aerospace industry to compensate for part variation due to the complex aerodynamic shapes of various assembled parts.
Manual shimming requires the parts to be installed and measured, fillers to be fabricated and installed, and gaps to be checked. Measuring gaps is a time-consuming process and fabricating the fillers after part installation requires additional production flow. In recent years, a process called predictive shimming has been developed to reduce the manufacturing time and cost associated with shimming activities. Predictive shimming typically involves measuring the mating surfaces of the parts prior to assembly, performing a virtual assembly of the parts, estimating the resulting gap between the parts, and then fabricating a filler prior to assembly. The filler (hereinafter “shim”) is designed to fill the gap between the mating parts.
While past predictive shimming efforts have used measurement data for virtual assembly, these processes only use measurements from the mating features, including holes or surfaces used to attach the parts, and merely minimize the gap between the parts. Previous predictive shimming processes use measurement data of mating surfaces to fill gaps. These processes have not focused on optimizing the final orientation of the parts, but rather merely seek to fill gaps between two parts. More specifically, previous predictive shimming efforts did not consider key features of the two parts. Key features are orientations and measurements specified by engineering requirements that must be satisfied after assembly of the parts is completed.
There is need for a method of locating and shimming one part relative to another part which is capable of taking into account a key feature of the one part.